This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Using small-angle x-ray scattering interference between gold nanocrystal labels, Mathew-Fenn et al. have measured the end-to-end length for a series of DNA double helices in solution. This newly developed Au-SAXS-based x-ray ruler provides the distance probability distribution of an ensemble of molecules. Thus, this technique provides a unique and powerful probe of macromolecular conformational heterogeneity. To establish this ability of this x-ray ruler technique, we propose to study the conformational flexibility and heterogeneity in DNA helices with bulged nucleotides. A-bulges have been shown to bend DNA, giving a good starting point for these studies, but the degree of underlying conformational heterogeneity is unknown. We will compare the effect of A and U bulges of length 1-5 on DNA bending and heterogeneity. We are applying for rapid access because Dr. Mathew-Fenn, the originator of this technique, will leave Stanford in mid-April and we would like to carry out initial SAXS experiments before her departure. Mathew-Fenn et al. have measured the end-to-end length for a series of DNA double helices in solution. This newly developed Au-SAXS-based x-ray ruler provides the distance probability distribution of an ensemble of molecules. Thus, this technique provides a unique and powerful probe of macromolecular conformational heterogeneity. To establish this ability of this x-ray ruler technique, we propose to study the conformational flexibility and heterogeneity in DNA helices with bulged nucleotides. A-bulges have been shown to bend DNA, giving a good starting point for these studies, but the degree of underlying conformational heterogeneity is unknown. We will compare the effect of A and U bulges of length 1-5 on DNA bending and heterogeneity.